This invention pertains to a photovoltaic device having a luminescent collector with at least one angular side extension and a cell mounted near or on the end edge surface of the side extension protected from the heat of the sun.
A typical photovoltaic solar panel has an array of photovoltaic cells interconnected with copper and mounted inside a metal frame of the type herein illustrated. An easily cleaned radiation transmissive cover sheet is used to protect the upper surface of the cells. The interstices between the cells may be covered with a reflective material to increase their efficiency. The voltage, current and wattage output of a photovoltaic cell decrease with increasing temperature. In the typical panel, the cells are directly exposed to the heat of the sun, whether the sunlight is direct or reflected. It has been proposed to use forced fluid cooling of solar cells, especially when the sunlight is concentrated by focusing or reflective devices, but this reduces the overall efficiency of the system and for many applications forced cooling is impractical.
It has been proposed, in for example, APPLIED OPTICS, Volume 15, No. 10, Pages 2299-2300, October 1976, the disclosure of which is incorporated herein by reference, to convert solar radiation to electrical energy with a solar cell comprised of a planar sheet of luminescent medium with edge coupled semiconductor photocells. The luminescent medium acts as an efficient collector of solar radiation. The collector is a flat sheet of material having parallel upper and lower surfaces. Solar radiation enters the collector through the upper or outer surface. The collector uses luminescent dyes or materials which are selected for their absorption properties, luminescent efficiency and transmittance in the emission region. The luminescent materials tend to absorb light energy in a portion of the solar spectrum. The luminescent materials reradiate the absorbed light energy at a better wavelength or energy form for conversion to electricity by a solar cell. The luminescent materials also radiate the absorbed light energy at an angle which facilitates internal reflection of the captured light energy and prevents loss of light energy from the collector. The surfaces of the collector are kept free of absorptive or nonreflective substances so that the surfaces tend to internally reflect the collected light energy. Much of the useful light energy is thus trapped in the collector and propagates to the edges of the collector where the light energy is emitted into one or more photovoltaic cells. Some of the collected light energy tends to be lost from the collector by successive reflections at the upper or lower surface. The capture properties of the collector have been enhanced by coating or covering the bottom surface of the collector with a mirror-like or diffusive type internal reflective coating. In addition, it has been proposed to use a filtering layer ahead of the upper surface of the collector to reflect or filter out undesired solar radiation.
The planar luminescent collector has edge mounted cells which are in the direct heat of the solar energy or close to surfaces directly heated by the sun. Cells are relatively fragile and difficult to interconnect. A solar panel using the flat luminescent collector with edge mounted cells is, therefore, difficult to manufacture in a sturdy, efficient way where the cells are kept relatively cool.
In this invention, the luminescent collector is angularly shaped and the photovoltaic cell is placed away from surfaces directly heated by the sun and is entirely shadowed from the solar source without loss of collecting area. The special shape of the collector also facilitates manufacture of the panel.